Ok.. So I am new to arduino... BUT I have dated experience with IC, and electronics... Read that as I was a digital/analog tech in the Marines working on Radars with everything from ICs to transistors and sealed circuits to high-power cross field amplifiers and travelling wave tubes... anyway....

I've decided to delve into an old project...

Here is my goal....Using an existing ISY994i home controller I would like to be able to do multiple control changes using 3 to 5 digit codes that upload via serial interface to the controller.

as I see it, I can get a 3x4 matrix keyboard, connect that to an arduino and then output to the serial INSTEON modem.on the surface that looks very straight forward..the challenge comes in where I want to format the serial output such that the serial communications will send the data from the keypad as a user bit in the INSTEON Message format..Pass the entire keyboard string to the serial output such that a # is the terminating input. so if I enter 341134456774# it sends all that or if I enter 323# it sends only that

So Is that as simple as I think? The format of the serial message is just programmed on the arduino? or should I look for another solution?

likely I would do this:Code starts with a number and ends with a #...then the number in the middle is the IF statement that starts a Macro on the ISY controller....